1. Field of the Invention
This invention relates generally to a system for estimating vehicle side-slip and, more particularly, to a system for estimating vehicle side-slip that uses vehicle lateral acceleration and vehicle-dependent parameters.
2. Discussion of the Related Art
Various vehicle stability control systems are known in the art that improve driver convenience, safety and comfort. These stability control systems typically employ differential braking and/or active front and rear wheel steering to provide the stability control. The stability control systems generally operate within a linear vehicle operating region, where vehicle states define the behavior of the vehicle. The vehicle states are generally determined from measured parameters, such as vehicle yaw rate, vehicle longitudinal velocity and vehicle lateral velocity.
Vehicle side-slip velocity is one of the key states for determining vehicle dynamics, kinematics and control for these types of stability control systems. Vehicle side-slip velocity is defined as the lateral speed at the vehicle's center of gravity in a direction perpendicular to the vehicle longitudinal velocity. The vehicle side-slip velocity combined with the vehicle longitudinal velocity defines a vehicle vector velocity in the vehicle traveling direction. However, the measurement of vehicle side-slip angle, which requires a measurement of vehicle side-slip velocity, requires special sensors that are very expensive. Therefore, vehicle stability control systems typically estimate vehicle side-slip velocity. Particularly, vehicle control systems calculate the vehicle side-slip velocity to determine an error so that the vehicle can be controlled to reduce the side-slip error to zero. However, vehicle side-slip velocity is difficult to accurately calculate because it is typically very small within the linear operating region of the vehicle.
One known method for estimating vehicle side-slip velocity that uses limited-bandwidth integration is disclosed in U.S. Pat. No. 6,819,998, titled Method and Apparatus for Vehicle Stability Enhancement System, issued Nov. 16, 2004 to Lin et al., assigned to the Assignee of this invention and herein incorporated by reference. As a result, reasonably accurate side-slip estimations can be provided without expensive side-slip velocity sensors. However, improvements can be made for estimating vehicle side-slip velocity.